1. Field of the Invention
This invention relates to a method for producing a seamless metallic belt, which is capable of use as a belt for a conveyor.
2. Description of the Related Art
Conventionally, an endless metallic belt, which is formed out of thin-plane shaped metallic material, is used for a belt of a conveyor.
This type of endless metallic belt is used for a belt for molding a synthetic resin film, a synthetic resin sheet, a synthetic resin board or the like. Particularly, a mirror belt finished to a mirror surface is used for producing an optical film, sheet, board or the like, that requires a very smooth surface.
As material of the aforementioned endless metallic belt, various metals are properly used especially, stainless material (SUS) inhabiting a generation of a rust and so on is heavily used for the mirror finished belt in order that evenness of the surface is not impaired.
The aforementioned endless metallic belts are produced with, for example by, a method in which a metallic plate processed by metal rolling is to be a banded shape and the endless belt is resulted by welding both of the ends of the banded metallic plate in another method in which a metallic pipe is formed, by metal rolling and the thin endless belt is resulted by enlarging the diameter of a loop of the metallic pipe, and so on. The endless belt produced with metal rolling is called as a seamless metallic belt or the like in view of no joint line like end-welding.
In the aforementioned conventional producing method, however, the following disadvantages are listed. Disadvantages of the producing method with end-welding for the banded metallic plate.
In the producing method with end-welding for the banded metallic plate, the mechanical strength of a welded portion is reduced to approximately 50-70% as compared with another portions of the main body. Thereby allowing disadvantages in which the welded portion becomes expanded (necking) with the use, and further, degradation, weld crack, rupture and so on easily appear by repeatedly bending.
In order to ensure long-lasting use of the endless belt with end-welding, it is required that the diameter of rollers run thereon with the endless belt is defined as more than 1,000 times of the thickness of the endless belt, curvature radius is defined to be larger so as not to concentrate large force on the welded portion, and so on. As a result, a disadvantage in which a device using the endless belt is not allowed to be small sized.
On the endless belt with end-welding, the welded portion becomes changed as compared with another portions of the main body and brought about necking over time even on the mirror finished belt, resulting in a disadvantage of faulty appearance, such as optical anisotropy and the like.
Disadvantages of the producing method with pipe metal rolling
In the producing method with pipe-metal rolling, there is a disadvantage of need of a large special apparatus in the manufacture.
In view of manufacturing with metal rolling of the pipe, there is a disadvantage in which it is difficult that the dimemsional accuracy of the thickness of the belt and the like is increased, particularly, it is seriously difficult that all the circumferential length of the belt is produced in high accuracy.
It is an object of the present invention to provide a method for producing a seamless metallic belt without a welded line and capable of being easily produced in high accuracy.